A light-emitting diode (LED) is a two-lead semiconductor light source comprising a pn-junction diode, which emits light when forward biased, where electrons from the semiconductor's conduction band recombine with holes from the valence band releasing sufficient energy to emits produce photons of a monochromatic (single color) of light. This effect is generally called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the band gap energy of the particular semiconductor material. A known way to control the brightness of LEDs is to use a control process technique known as “Pulse Width Modulation” (PWM) in which the LED is repeatedly turned “ON” and “OFF” at varying frequencies by a suitable PWM controller control signal depending upon the required light intensity.
LED panels (or arrays) are capable of generating relatively high amounts of light (high luminance), which allows video displays having LED panels to be used in a variety of ambient conditions. However, LEDs are known to be subject to a ghost lighting effect where ghost images result when though a current path through intended OFF LEDs adjacent to ON LEDs, which causes very faint illumination or “ghosting” of the intended OFF LEDs. These ghost-image currents typically result from the discharging of stray capacitances associated with the large, common-LED anode-node tracks and the slightly forward-biased LEDs themselves. To reduce ghost lighting problems a pre-charge circuit can be added to an LED driver for pre-charging an output node of the respective columns to a fixed target voltage when triggered by an ON/OFF control signal received from a controller, such as to a fixed pre-charge voltage of about Vcc-1.4V.